Emergency brake assistance systems (EBA) based on environment sensor systems and which are currently available on the market assist drivers of a vehicle when there is the risk of a rear-end collision and the driver reacts too late or incorrectly, or not at all. Assistance can be provided by activating a visual, acoustic and/or haptic warning, by a (partially) autonomous braking intervention or during a braking intervention by the driver.
The speed range within which such systems are generally active is typically between 30 km/h and 180 km/h (CMS: Collision Mitigation Brake System; CMBB: Collision Mitigation By Braking; CMBS: Collision Mitigation Brake System by car manufacturer Honda).
Recently, systems have appeared on the market which are already active from approximately 0 km/h, for example the Pre-Safe brake used in the S-class range by car manufacturer Mercedes-Benz or the City Safety system by car manufacturer Volvo (such as in the XC60 model), which is active from approximately 0 km/h to approximately 30 km/h.
One key factor in the system design of emergency brake assistance systems is the avoidance of and dealing with erroneous activations. Due to the deficits of environment sensor systems and interpretation, such activations cannot be ruled out, in particular since the signal quality of the environment sensor system is generally only categorised as QM (Quality Management), i.e. as not relevant to safety as specified in ISO 26262; at the most, it is categorised as ASIL (Automotive Safety Integrity Level) level A as specified in ISO 26262.
Erroneous activations can occur depending on the environment sensor system used, in particular at low speeds. In addition, depending on the environment sensor system used, objects which are a priori at standstill present problems, and may be the cause of an erroneous activation. This applies in particular to the radar sensor systems generally used today for emergency brake assistance systems.
Driver reactions and predicted actions such as steering, indicating, braking and accelerating are also incorporated in the activation and cancellation concept of emergency brake assistance systems.
A further safety concept is that, when an intention to cancel is detected, or a traffic situation is detected in which it cannot be assumed that an intention to activate will arise, activation must be cancelled or suppressed. This safety target is classified as SIL3 according to the SIL (Security Integrity Level) standard or ASIL level D, and is recognised throughout the industry. Both a cancellation and a suppression of activation generally occur when the driver actuates the accelerator in the positive direction. An intention to accelerate or set the vehicle in motion on the part of the driver is interpreted as “not intending to brake”, in particular when “kick-down” is in operation (the driver treads fully on the accelerator). For this purpose, the gradient and/or absolute value of the accelerator activation is in most cases evaluated on the basis of an interpretation threshold.